This invention relates to a controllably bendable tube assembly, especially a hollow steering section of a borescope or endoscope.
An endoscope is generally characterized as an elongated flexible tube with a viewing head in its distal or forward end, and a control housing at its proximal end for controlling or steering the distal end. In such an endoscope, a bendable tube section is provided at the distal end adjacent to the viewing head. One or two pairs of control cables extend through the bendable tube section and the remainder of the flexible tube and connect with a steering control in the control section. One, or both pairs of these cables are displaced in order to bend the bendable section to facilitate the inspection of an object.
An endoscope is typically inserted into the cavity of a patient in order to visually investigate the tissues within the cavity. For example, an endoscope can be inserted into the colon, stomach, or into the lung of a patient. Because the esophagus, bronchii and the colon are narrow, tortuous passageways, the steering section must be bent rather precisely, and as close to the head as possible, in order to obtain the necessary penetration without damaging the patient's tissues. It is most desirable that the bending take place as close to the viewing head as the steering section is bent in a full arch or in a partial arch, and it is also most desirable that the play or slop in the cable be kept to a minimum.
A borescope is a similar device, but intended for visual inspection of a mechanical device, such as a jet engine or turbine, where it would be difficult or impossible to examine the device's internal elements. The borescope needs to be insertable into narrow tortuous passageways, and must observe similar steering and bending considerations.
A number of types of steering mechanisms are known. For example, helically coiled strips are employed in endoscopes or borescopes as descibed in U.S. Pat. Nos. 3,610,231 and 3,739,770. Steering sections having thin walled cylindrical segments or bands that are joined by means of pins or bifurcations, or other similar articulations such that the segments are rockable on one another, are described in U.S. Pat. Nos. 3,583,393; 3,669,098; 3,799,151; and 4,347,837. A previously-proposed endoscope that had a provision to control the degree of bending is described in U.S. Pat. No. 3,557,780. In that endoscope, the steering section was formed of two flexure portions, and had two sets of control wires. Stays or flexible backbone members of various lengths were employed so that the degree of curving and the location of the curvature on the steering portion could be controlled.
In the endoscope described in the U.S. Pat. No. 3,799,151, cylindrical segments were articulated in one plane or in another plane as required to select the amount and direction of bending of the endoscope steering portion.
From a consideration of the foregoing, it becomes apparent that the steering mechanisms for these previously-proposed endoscopes are rather elaborate structures, with many parts that can fail and which are relatively expensive to produce. Also, in the case of steering sections which are bendable in two planes, it has been necessary to provide the cables with a significant amount of slop or play, because the steering sections bend at discrete points, and not in a perfectly smooth curve.